Conductive screen for cathode ray tubes

ABSTRACT

A conductive screen formed of a frame and a series of electrically conductive fibers. The screen is fitted over the display surface of a cathode ray tube (CRT) and connected to ground wire to diffuse emanated radiation and static electricity.

BACKGROUND OF THE INVENTION

This invention relates to a microwave screen and will have specialapplication to a conductive screen which suppresses static electricityand electromagnetic radiation output of a video display terminal.

Recently, there has been a rapid increase in the use of video displayterminals (VDT's) and the like. It has been shown that the surface ofthe cathode ray tube (CRT) in a VDT reflects glare from the surroundingenvironment which, in many instances, causes the user to experience eyefatigue and headache. A framed mesh screen of black filaments disclosedin U.S. Pat. No. 4,253,737 has been introduced to overcome the glareproblem.

A potentially more serious problem with VDT's is their tendency togenerate an electrostatic field adjacent to the CRT. This problem hasrecently been classified as a potential health hazard. In fact, manyfacial rash cases among VDT operators have been reported. This isattributable to the operator becoming electrically charged in theelectrostatic field of the CRT so that dust and other pollutants, suchas bacteria or other irritants, of opposite charge are attracted to theoperator. The dust carrying opposite charge may also be attracted to thesurface of the CRT and pollute the VDT screen as a result of the inducedstatic charge.

The risk of nonionizing radiation in VDT screens has been debated forseveral years. It was reported that current levels of electromagneticradiation which emanate from the CRT are well below the level at whichthe operator may become injured. However, such radiation does exist andolder VDT's and those in a worsened condition most likely will produceradiation at levels which exceed the FDA standard allowed for televisionsets. At present, low frequency radiation is eliminated by a stainlesssteel (or other metal) mesh screen sandwiched between two rigid panelsplaced in front of the VDT screen. Due to the space between the screensand the display tubes, such devices produce Newton rings and Moriedistortions. Mesh screens designed to eliminate such distortions areshown in U.S. Pat. Nos. 4,253,737 and 4,468,702.

As disclosed above, the screen of U.S. Pat. No. 4,253,737 was introducedto overcome the glare problems. The nylon screen disclosed in U.S. Pat.No. 4,468,702 is formed of a plurality of nylon yarns, some of which areelectrically conductive. However, the method of making this screen isquite complicated and produces screen where only a fraction of the warpand weft fibers of the screen are electrically conductive.

SUMMARY OF THE INVENTION

The electrically conductive screen of this invention is formed bytreating fibers, such as nylon or polyester, in a bath which containscopper (II) sulfide and an acid. Carbon black powder may also be addedto the bath. As a result, all of the interwoven yarns of the screen arerendered conductive. The screen is then mounted in a flexible frame. Aground wire is attached to the frame prior to attaching the screen tothe front surface of a VDT. By forming the screen of a series ofconductive yarns, the emanation of electromagnetic radiation and staticelectricity from the VDT is significantly reduced.

Accordingly, it is an object of this invention to provide an improvedscreen which is for a video display terminal.

Another object of this invention is to provide for a VDT screen in whichsubstantially all of the screen yarns are electrically conductive.

Another object of this invention is to provide for a VDT screen whichreduces glare and effectively suppresses emanation of electromagneticradiation and static electricity about the surface of a cathode raytube.

Another object of this invention is to provide for a VDT screen which issimple and economical to produce.

Other objects of this invention will become apparent in a reading of thefollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention has been depicted forillustrative purposes wherein:

FIG. 1 is a perspective view of a VDT showing the screen of thisinvention in use.

FIG. 2 is a front elevational view of the screen.

FIG. 3 is a rear elevational view of the screen.

FIG. 4 is a fragmentary detail view of the rear portion of the screenshown in broken line 4 of FIG. 3.

FIG. 5 is a fragmentary sectional view taken along line 5--5 of FIG. 2.

FIG. 6 is a fragmentary elevational view of the rear portion of thescreen shown in broken line 6 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment herein described is not intended to beexhaustive or to limit the invention to the precise form disclosed. Itis chosen and described to explain the principles of the invention andits application and practical use to enable others skilled in the art toutilize the invention.

Referring to the drawings, FIG. 1 depicts a static electricity andradiation elimination member 12 incorporated in a video display terminal(VDT) 8 which has a cathode ray tube (CRT) 10. Member 12 includes anelectrically conductive screen 14 secured to a flexible frame 15 byconductive polymeric strip 18 (FIG. 4), and an adhesive strip 17. Aground wire 16 extends from inside CRT 10 and is attached to frame 15 bya nut 19 and bolt 20 combination.

Frame 15 includes a front frame part 15' and a rear frame part 15" asshown in FIG. 5. Frame parts 15' and 15" are joined at their end edges 9to form frame 15. Screen 15 is formed of fibers which range from 0.002inches to 0.0028 inches in diameter and a mesh count of 109 to 200filaments per inch to provide mesh openings of 0.003 to 0.006 inches. Asindicated in U.S. Pat. No. 4,253,737, incorporated herein by reference,screen 14 is mounted in frame 15 and maintains contact over the displaysurface 27 of the CRT 10 to eliminate the distortions in Newton ringsand Morie patterns.

Screen 14 is formed by treating fine mesh fabric, preferably nylon orpolyester, in a heated bath which contains copper (II) sulfide and anacid. Carbon black powder may be added to the bath as a catalyst. Thecopper sulfide is adsorbed onto the fibers to render screen 14 highlyconductive, which allows the screen to function as a static electricityand radiation elimination device. Also, the screen 14 may be dyed withan anti-reflective color such as dark grey or black to reduce glare. Themethod of forming screen 14 is described in detail in U.S. Pat. No.4,661,376, issued Apr. 28, 1987, which is incorporated herein byreference.

After screen 14 has been thus formed, it is fitted into frame part 15'and secured by adhesive 17 as shown in FIG. 4. Bolt 20 is then passedthrough a bore 21 in frame part 15' and secured to frame part 15' incontact with screen 14 by nut 19. Frame part 15" is then secured toframe part 15' as above noted. A depression 24 in frame part 15" (FIG.5) accommodates screw 20. This connection allows a continuous currentflow between ground wire 16 and screen 14 whereby static electricity andradiation are effectively diffused.

It is understood that the above description does not limit the inventionto the details above given but may be modified within the scope of theappended claims.

I claim:
 1. An electrically conductive radiation elimination deviceadapted for use with a cathode ray tube, said device comprising a frame,a screen formed entirely of non-metallic fibers chemically treated witha metallic compound wherein the fibers are rendered electricallyconductive, said screen fitted in said frame.
 2. The radiationelimination device of claim 1 wherein said frame includes first andsecond joined frame parts, means securing said screen between said frameparts.
 3. The radiation device of claim 2 wherein said securing meansincludes an electrically conductive strip affixed to said frame, anelectrically conductive bolt extending through said first frame part andcontacting said screen, said bolt constituting means for electricallyconnecting said device to a ground wire.
 4. The device of claim 1wherein said fibers are polyester mesh fabric coated with copper (II)sulfide.
 5. In combination, a video display terminal including a cathoderay tube and a ground wire, and a radiation elimination devicepositioned between said cathode ray tube and a user, said radiationelimination device comprising a frame, a screen formed entirely ofnon-metallic fibers which have been chemically treated with a metalliccompound to render said fibers electrically conductive, said screensecured in said frame, means for connecting said screen to said groundwire for diffusing static electricity and electromagnetic radiationemanating from said cathode ray tube.
 6. The combination of claim 5wherein said frame includes first and second joined frame parts, meanssecuring said screen between said frame parts.
 7. The combination ofclaim 6 wherein said securing means includes an electrically conductivestrip affixed to said frame, an electrically conductive bolt extendingthrough said first frame part and contacting said screen, said boltconstituting means for electrically connecting said device to a groundwire.